The invention relates to an adhesive topcoated multi-filament polyester and to the process of incorporating the same into rubber. More specifically, the invention relates to a multi-filament polyester fibrous material topcoated with an active isocyanate containing composition and which can be processed without the problems normally attendant the use of active isocyanates.
Polyester fibers, cords and fabrics are used extensively for reinforcing rubber articles such as tires, belts, hoses and the like. But, polyester textile elements generally adhere poorly to rubber unless first treated to improve adhesion, as by coating. Because of the exceptional strength and reinforcing ability of polyester fibers, there has been a continuous effort to improve the adhesion of polyesters to rubber.
One widely used process for adhering polyester to rubber involves coating polyester with a latex material containing resorcinol-formaldehyde resin. Such latexs are well known to those skilled in the art as "RFL" latexes or dips. RFL coated polyesters are first heated and then a layer of rubber is applied to and cured on the thus treated polyester. But, this system can be unsatisfactory depending on various factors such as the degree of polyester heat treatment; the composition of the polyester substrate; the amount of stress or heat the reinforced rubber article undergoes; and the like.
Many types of treatments for improving polyester to rubber bonding, e.g., surface coatings, adhesive formulations, and the like have been tried. But each has suffered from one or more disadvantages. It has been proposed to topcoat polyester multi-filament material with an active isocyanate containing composition prior to RFL dipping. But, the high reactivity of isocyanate materials, particularly in the presence of moisture, has been a shortcoming to this system. When an isocyanate topcoat has been applied to polyester prior to twisting of filaments into cord, material buildup on twisting rolls has been a severe problem. Additionally, it has been reported that isocyanate pretreatment followed by RFL treatment provides polyester material exhibiting good bonding to rubber at low temperatures, but suffering degradation at elevated temperatures, particularly in the presence of moisture.